Black Carbon Mass Concentration Research Articles

Changes in black carbon and PM2.5 in Tokyo in 2003-2017.

Black carbon (BC) particles cause adverse health effects and contribute to the heating of the atmosphere by absorbing visible solar radiation. Efforts have been made to reduce BC emissions, especially in urban areas; however, long-term measurements of BC mass concentration (MBC) are very limited in Japan. We report MBC measurements conducted in Tokyo from 2003 to 2017, showing that MBC decreased by a factor of 3 from 2003 to 2010 and was stable from 2010 to 2017. Fine particulate concentrations (PM2.5) decreased by a much smaller factor during 2003–2010. The diurnal variations of BC size distributions suggest that the BC in Tokyo originates mainly from local sources, even after 2010. Our three-dimensional model calculations show that BC from the Asian continent contributes a small portion (about 20%) of the annual average MBC in the Kanto region of Japan, which includes Tokyo. This indicates that continued reduction of BC emissions inside Japan should be effective in further decreasing MBC.

Study of spectral characteristics of black carbon from biomass burning and source apportionment over Agartala in the northeastern India.

We have studied the black carbon (BC) mass concentrations, contributions from Fossil Fuels (FF), and Biomass burning (BB) to total BC mass concentrations using a 7-wavelength Aethalometer (Model, AE-31; Make, Magee Scientific, USA) at a rural continental location in the northeastern India. We have taken the continuous measurements of BC from January 2011 to December 2017 (excluding the year 2016 due to nonavailability of data). The annual mean BC concentration at 880 nm is observed maximum 12.56±5.06 µgm-3 in the year 2011 with a minimum of 7.26±2.76 µgm-3 during the year 2015." is the final sentence. BC, BCff, and BCbb mass concentrations show significant variation during morning, afternoon, evening, and night hours. The significant monthly, seasonal, and annual variabilities in the BC concentration, equivalent BC from FF and BB, are due to seasonal change in the emission sources, boundary layer dynamics, and dispersion and dilution conditions. The determination of Angstrom exponent (α) for the BC emitted during burning of different biofuels by performing a burning experiment is an important part of the present study. We have conducted a survey in and around the study location to know the different biofuels used by the people for daily household activities, and those biofuels are used in the burning experiment. As a result of biomass burning experiment to determine Angstrom exponent, we have found the α values to be ranging from 1.20 to 2.37 for flaming and a range from 1.59 to 2.33 for smoldering conditions for different biofuels. Annual mean contributions of BCff and BCbb to the total BC are found to be dominated by FF emissions during the whole study period. The percentage contribution of BCff and BCbb is found to be 56% and 44% during winter season due to increase in wood and biomass burning activities for various purposes. We have found the higher percentage contribution from BCff (85%) during monsoon season due to reduction in usage of biofuels.

Trends and source apportionment of aerosols in Europe during 1980–2018

Abstract. Aerosols have significantly affected health, environment, and climate in Europe. Aerosol concentrations have been declining since the 1980s in Europe, mainly owing to a reduction of local aerosol and precursor emissions. Emissions from other source regions of the world, which have been changing rapidly as well, may also perturb the historical and future trends of aerosols and change their radiative impact in Europe. This study examines trends of aerosols in Europe during 1980–2018 and quantifies contributions from 16 source regions using the Community Atmosphere Model version 5 with Explicit Aerosol Source Tagging (CAM5-EAST). The simulated near-surface total mass concentration of sulfate, black carbon, and primary organic carbon had a 62 % decrease during 1980–2018. The majority of which was contributed to reductions of local emissions in Europe, and 8 %–9 % was induced by a decrease in emissions from Russia–Belarus–Ukraine. With the decreases in the fractional contribution of local emissions, aerosols transported from other source regions are increasingly important for air quality in Europe. During 1980–2018, the decrease in sulfate loading led to a warming effect of 2.0 W m−2 in Europe, with 12 % coming from changes in non-European sources, especially from North America and Russia–Belarus–Ukraine. According to the Shared Socioeconomic Pathways (SSP) scenarios, contributions to the sulfate radiative forcing over Europe from both local European emissions and non-European emissions should decrease at a comparable rate in the next 3 decades, suggesting that future changes in non-European emissions are as important as European emissions for causing possible regional climate change associated with aerosols in Europe.

Evaluation of black carbon mass concentrations using a miniaturized aethalometer: Intercomparison with a continuous soot monitoring system (COSMOS) and a single-particle soot photometer (SP2)

Ground-based observations of black carbon (BC) aerosols were conducted in spring 2017 in Yokosuka City, south of Tokyo, Japan. Equivalent BC (EBC) mass concentrations were measured using a miniaturized, palm-sized filter-photometer (MicroAeth AE51, EBCAE51) and evaluated against those obtained using a continuous soot monitoring system (COSMOS, EBCCOSMOS) and a single-particle soot photometer (SP2, refractory BC, rBCSP2). We propose methods to account for the following key factors affecting AE51 measurements: (1) the non-linearity of light attenuation (ATN) measurements associated with high-particle loading on the filter (i.e., the loading effect); and (2) the positive artifacts in ATN measurements created by non-refractory materials (nonBC) on the filter. To examine these effects, we employed a custom automated system that switches the two sampling lines for the AE51, one of which was heated to 300 °C to minimize the sampling of nonBC. Alternate operation of the heated and unheated modes (for 15 min) enabled the separation of the described effects. Consistent with previous studies, in the heated mode, sensitivity decreased linearly with increases in ATN (−0.44% per ATN) in comparison with the other aethalometers. When the loading effect was corrected for, the EBCAE51 in the unheated mode still showed some bias relative to EBCCOSMOS and rBCSP2. This bias correlated with—and was successfully corrected for using—the mass ratio of nonBC to BC derived from the SP2. This approach can also be applied to fine-mode aerosol (PM2.5) concentrations measured at environmental monitoring networks, thus eliminating the need for additional SP2 data in the data correction.

How emissions uncertainty influences the distribution and radiative impacts of smoke from fires in North America

Abstract. Fires and the aerosols that they emit impact air quality, health, and climate, but the abundance and properties of carbonaceous aerosol (both black carbon and organic carbon) from biomass burning (BB) remain uncertain and poorly constrained. We aim to explore the uncertainties associated with fire emissions and their air quality and radiative impacts from underlying dry matter consumed and emissions factors. To investigate this, we compare model simulations from a global chemical transport model, GEOS-Chem, driven by a variety of fire emission inventories with surface and airborne observations of black carbon (BC) and organic aerosol (OA) concentrations and satellite-derived aerosol optical depth (AOD). We focus on two fire-detection-based and/or burned-area-based (FD-BA) inventories using burned area and active fire counts, respectively, i.e., the Global Fire Emissions Database version 4 (GFED4s) with small fires and the Fire INventory from NCAR version 1.5 (FINN1.5), and two fire radiative power (FRP)-based approaches, i.e., the Quick Fire Emission Dataset version 2.4 (QFED2.4) and the Global Fire Assimilation System version 1.2 (GFAS1.2). We show that, across the inventories, emissions of BB aerosol (BBA) differ by a factor of 4 to 7 over North America and that dry matter differences, not emissions factors, drive this spread. We find that simulations driven by QFED2.4 generally overestimate BC and, to a lesser extent, OA concentrations observations from two fire-influenced aircraft campaigns in North America (ARCTAS and DC3) and from the Interagency Monitoring of Protected Visual Environments (IMPROVE) network, while simulations driven by FINN1.5 substantially underestimate concentrations. The GFED4s and GFAS1.2-driven simulations provide the best agreement with OA and BC mass concentrations at the surface (IMPROVE), BC observed aloft (DC3 and ARCTAS), and AOD observed by MODIS over North America. We also show that a sensitivity simulation including an enhanced source of secondary organic aerosol (SOA) from fires, based on the NOAA Fire Lab 2016 experiments, produces substantial additional OA; however, the spread in the primary emissions estimates implies that this magnitude of SOA can be neither confirmed nor ruled out when comparing the simulations against the observations explored here. Given the substantial uncertainty in fire emissions, as represented by these four emission inventories, we find a sizeable range in 2012 annual BBA PM2.5 population-weighted exposure over Canada and the contiguous US (0.5 to 1.6 µg m−3). We also show that the range in the estimated global direct radiative effect of carbonaceous aerosol from fires (−0.11 to −0.048 W m−2) is large and comparable to the direct radiative forcing of OA (−0.09 W m−2) estimated in the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC). Our analysis suggests that fire emissions uncertainty challenges our ability to accurately characterize the impact of smoke on air quality and climate.

Temporal Evolution and Main Influencing Factors of Black Carbon Aerosol in Nanjing

Temporal evolution of black carbon (BC) in Nanjing was studied along with its main influencing factors. The multi-wavelength aethalometer (AE-33) was used to select the typical month of each season to observe BC mass concentration, combined with atmospheric pollutant data, meteorological elements, and boundary layer detection data. Seasonal, daily, weekly trends, and source characteristics of BC were analyzed. The results showed that the BC concentration in Nanjing had obvious seasonal changes, which were higher in spring and winter, in the decreasing order:spring[(3351±919) ng·m-3] > winter[(3234±2102) ng·m-3] > in autumn[(3064±967) ng·m-3] > summer[(2632±1705) ng·m-3]. The diurnal changes in BC during the four seasons are bimodal, with peaks at 06:00-08:00 and 21:00-23:00. The morning and evening peak distribution characteristics of BC in different seasons are different. The peak concentration of BC was highest in the early morning peak spring and the highest in the late peak winter. The morning peak timing of winter is 2 h behind other seasons, while the summer peak timing is 2 h ahead of other seasons. The effect of the wind speed on the seasonal distribution of BC diurnal variation is significantly larger than that on RH. The mechanism of the influence of the inversion layer on the concentration of atmospheric pollutants is complicated. The effects of height, thickness, and temperature of the inversion layer on the pollutants are different in different seasons. Weekly BC effects vary seasonally. The effect of RH and wind speed on the weekly BC effect is small, and the difference in the inversion layer is the main reason behind it. Liquid fuel combustion in Nanjing has a greater contribution to BC, whereas solid combustion contributes by a lesser extent.

Google Earth Engine–assisted black carbon radiative forcing calculation over a heavy industrial city in China

Black carbon (BC) aerosol has a low content in the atmosphere; however, it has a strong radiative forcing effect and a significant impact on human beings and the environment. BC aerosol radiative forcing (ARF) has a major environmental influence. The main method to calculate the ARF is numerical simulation using a radiation transfer model by inputting atmospheric and surface parameters. Currently, most research studies directly apply the albedo products, which are not the real surface albedo (the blue-sky albedo). Alternatively, they use an empirical formula to calculate the sky diffuse light ratio to obtain the real surface albedo. To overcome these shortcomings, this study develops a new scheme to obtain the BC ARF in Xuzhou City from May 2014 to July 2016 by combining the BC mass concentration, albedo measurements from the Google Earth Engine (GEE) platform, aerosol optical depth (AOD), and microphysical parameters retrieved from the Aerosol Robotic Network (AERONET). Although BC AOD accounts for 3.3 to 17.9% of the total AOD, the BC ARF at the surface (SFC) and top of the atmosphere (TOA) is between − 14.06 ± 4.645 W/m2 and − 4.04 ± 0.437 W/m2 and between 2.93 ± 1.034 W/m2 and 0.74 ± 0.093 W/m2, with average values of − 9.67 ± 2.787 W/m2 and 2.02 ± 0.587 W/m2, respectively. Finally, comparing the BC ARF obtained by different albedo methods shows that the BC ARF change at the TOA is marked, and generally, the BC ARF calculated by the empirical formula method is lower than that calculated by using the blue-sky albedo method.

Concentrations and Size Distributions of Black Carbon in the Surface Snow of Eastern Antarctica in 2011

AbstractKnowledge of black carbon (BC) concentrations and size distributions within surface snow in Antarctica is limited. However, these measurements are important to understanding global aerosol transport from combustion sources, and BC contributes to positive radiative forcing. This study analyzed the concentrations and size distributions of BC and inorganic ions in snow samples collected at the Syowa station in Antarctica from April to December 2011 and along a traverse route to an inland (Mizuho) station. The BC size distributions in snow were bimodal with mass median diameters of ~140 and ~690 nm. We also estimated the mass median diameter from unimodal distributions and found smaller diameters than were reported by other studies. The mass concentrations of BC in snow were higher in inland samples than in Syowa samples. Among Syowa samples, the BC concentrations in December (2117.3 ng L−1 on average) were higher than in other periods (288.2 ng L−1 on average). The December samples experienced ambient temperatures above 0 °C, and the atmospheric BC concentrations did not increase simultaneously. Inorganic ions originated from the ocean and decreased with increasing distance from the coastal area. We conclude that the BC concentrations in surface snow increased mainly by postdeposition processes through the loss of water mass due to melting, evaporation, and sublimation. Our study is the first to report detailed BC concentrations and size distributions in eastern Antarctica, and the results will help to evaluate BC global transport, the snow albedo estimations in this region, and the climate impacts of BC.

Wood smoke black carbon from Indigenous traditional cultural activities in a subarctic Cree community

ABSTRACT Indoor concentrations of black carbon (BC) were measured when wood was burned for traditional cultural activities in a study in a Cree community located in subarctic Canada. The study also included an intervention using a propane-fuelled heater to mitigate in situ BC. Mass concentrations of BC were measured in a game-smoking tent for 39 days and in hunting cabins on the west coast of James Bay, Canada, for 8 days. Five-minute averaged BC mass concentration (N = 12,319) data were recorded and assessed using optimised noise-reduction averaging. Mean BC mass concentrations were lower in hunting cabins (mean = 8.25 micrograms per cubic metre (µg m−3)) and higher in the game-smoking tent (mean = 15.46 µg m−3). However, excessive BC peaks were recorded in the game-smoking tent (maximum = 3076.71 µg m−3) when the fire was stoked or loaded. The intervention with the propane heater in a hunting cabin yielded a 90% reduction in measured BC mass concentrations. We do not presume that exposure to BC is of concern in hunting cabins with appropriate wood-burning appliances that are well-sealed and vent outside. In game-smoking tents, we advise that persons take intermittent breaks outside of the tent for fresh air.

Performance of microAethalometers: Real-world Field Intercomparisons from Multiple Mobile Measurement Campaigns in Different Atmospheric Environments

ABSTRACT Small aethalometers are frequently used to measure equivalent black carbon (eBC) mass concentrations in the context of personal exposure and air pollution mapping through mobile measurements (MM). The most widely used is the microAethalometer (AE51). Its performance in the laboratory and field is well documented, however, there is not sufficient data in the context of its performance in different environments. In this investigation, we present the characterization of the performance of the AE51 through field unit-to-unit intercomparisons (IC), and against a reference absorption photometer from three MM campaigns conducted in drastically different environments. Five IC parameters were considered: i) study area, ii) location of IC, iii) time of day, iv) duration of IC, and v) correction for the filter-loading effect. We can conclude that it is crucial where and how long the IC have been performed in terms of the correlation between the mobile and reference instruments. Better correlations (R2 > 0.8, slope = 0.8) are achieved for IC performed in rural, and background areas for more than 10 minutes. In locations with more homogenous atmosphere, the correction of the loading effect improved the correlation between the mobile and reference instruments. In addition, a newer microAethalometer model (MA200) was characterized in the field under extreme cold conditions and correlated against another MA200 (R2 > 0.8, slope ≈ 1.0), AE51(R2 > 0.9, slope ≈ 0.9), and a stationary Aethalometer (AE33) across all wavelengths (R2 > 0.8, slope ≈ 0.7). For MA200, the loading effect was more pronounced, especially at the lower wavelengths, hence the correction of the loading effect is essential to improve the correlation against the AE33. The MA200 and AE51 proved to be robust and dependable portable instruments for MM applications. Real-world quality assurance of these instruments should be performed through field IC against reference instruments with longer durations in areas of slowly changing eBC concentration.

Airborne survey of trace gases and aerosols over the Southern Baltic Sea: from clean marine boundary layer to shipping corridor effect

The influence of shipping on air quality over the Southern Baltic Sea was investigated by characterizing the horizontal and vertical distribution of aerosols and trace gases using airborne measurements in the summer of 2015. Generally, continental and anthropogenic emissions affected the vertical distribution of atmospheric pollutants, leading to pronounced stratification in and above the marine boundary layer and controlling the aerosol extinction. Marine traffic along the shipping corridor “Kadet Fairway” in the Arkona Basin is shown to influence the presence and properties of both trace gases and aerosol particles in the lowest atmospheric layer. Total particle number concentration and NOy mixing ratio increased in the corridor plumes, relative to background, by a factor 1.55 and 3.45, respectively. Titration, triggered by the enhanced presence of nitrogen compounds, led to a median ozone depletion of 19% in the corridor plumes. The enforcement of the Sulphur Emission Control Area (SECA) might be responsible for the minor sulphur dioxide increase (20%) in the corridor plumes. Ship traffic caused a minor enhancement of black carbon mass concentration, estimated to be around 10%. The study of individual ship plumes indicated that ship emitted aerosol was substantially different from background aerosol: fresh ship exhaust was preferentially enriched in aerosol particles with diameters below 100 nm and in black carbon particles with core diameters above 300-400 nm. With the present work the impact of marine traffic on the concentration and properties of atmospheric components within the marine boundary layer over the open water of the Southern Baltic Sea is assessed with airborne observations for the first time. Due to the high uncertainty affecting the estimations of ship emissions, this dataset represents a valuable reference for the assessment of ship emission inventories and related environmental-climatic impacts on the Southern Baltic Sea.

서울 여름철 내화성 블랙카본의 질량과 입경분포 분석

서울 여름철 내화성 블랙카본의 질량과 입경분포 분석

Aerosol and Its Radiative Effects during the Aeroradcity 2018 Moscow Experiment

During the AeroRadCity-2018 spring aerosol experiment at the Moscow State University Meteorological Observatory the aerosol properties of the atmosphere and radiative aerosol effects were analyzed using a wide complex of measurements and model COSMO-ART simulations over Moscow domain. The program of measurements consisted of columnar aerosol AERONET retrievals, surface PM10, black carbon (BC) and aerosol gas precursors mass concentrations, as well as radiative measurements under various meteorological conditions. We obtained a positive statistically significant dependence of total and fine aerosol optical depth (AOD) mode (R2 ~0.4) with PM concentrations. This dependence has revealed a pronounced bifurcation point around PM10=0.04 mgm-3. The modelled BC concentration is in agreement with the observations and has a pronounced correlation with PM, but not with the AODs. The analysis of radiative effects of aerosol has revealed up to 30% loss for UV irradiance and 15% - for shortwave irradiance at high AOD in Moscow. Much intensive radiation attenuation is observed in the afternoon when remote pollution sources may affect solar fluxes at elevated boundary layer conditions. Negative (cooling) radiative forcing effect at the top of the atmosphere from -18 Wm-2 to -4 Wm-2 has been evaluated. Mean difference in visible AOD between urban and background conditions in Moscow and Zvenigorod was about 0.01 according to measurements and model simulations, while in some days the difference may increase up to 0.05. The generation of urban aerosol was shown to be more favorable in conditions with low intensity of pollutant dispersion, when mean deltaAOD550 was doubled from 0.01 to 0.02.

Black carbon aerosol quantification over north-west Himalayas: Seasonal heterogeneity, source apportionment and radiative forcing

Continuous measurements of Black Carbon (BC) aerosol mass concentrations were carried at Dehradun (30.33°N, 78.04°E, 700 m amsl), a semi-urban site in the foothills of north-westHimalayas, India during January 2011–December 2017. We reported both the BC seasonal variations as well as mass concentrations from fossil fuel combustion (BCff) and biomass burning (BCbb) sources. Annual mean BC exhibited a strong seasonal variability with maxima during winter (4.86 ± 0.78 μg m−3) followed by autumn (4.18 ± 0.54 μg m−3), spring (3.93 ± 0.75 μg m−3) and minima during summer (2.41 ± 0.66 μg m−3). Annual averaged BC mass concentrations were 3.85 ± 1.16 μg m−3 varying from 3.29 to 4.37 μg m−3 whereas BCff and BCbb ranged from 0.11 to 7.12 μg m−3 and 0.13–3.6 μg m−3. The percentage contributions from BCff and BCbb to total BC are 66% and 34% respectively, indicating relatively higher contribution from biomass burning as compared to other locations in India. This is explained using potential source contribution function (PSCF) and concentration weighted trajectories (CWT) analysis which reveals the potential sources of BC originating from the north-west and eastern parts of IGP and the western part of the Himalayas that are mostly crop residue burning and forest fire regions in India. The annual mean ARF at top-of-atmosphere (TOA), at surface (SUR), and within the atmosphere (ATM) were found to be −14.84 Wm−2, −43.41 Wm−2, and +28.57 Wm−2 respectively. To understand the impact of columnar aerosol burden on ARF, the radiative forcing efficiency (ARFE) was estimated and averaged values were −31.81, −91.63 and 59.82 Wm−2 τ−1 for TOA, SUR and ATM respectively. The high ARFE within the atmosphere indicates the dominance of absorbing aerosol (BC and dust) over Northwest Himalayas.

Black carbon physical and optical properties across northern India during pre-monsoon and monsoon seasons

Abstract. Black carbon (BC) is known to have major impacts on both climate and human health and is therefore of global importance, particularly in regions close to large populations that have strong sources. The size-resolved mixing state of BC-containing particles was characterised using a single-particle soot photometer (SP2). The study focusses on the Indo-Gangetic Plain (IGP) during the pre-monsoon and monsoon seasons. Data presented are from the UK Facility for Airborne Atmospheric Measurements BAe-146 research aircraft that performed flights during the pre-monsoon (11 and 12 June) and monsoon (30 June to 11 July) seasons of 2016. Over the IGP, BC mass concentrations were greater (1.95 µg m−3) compared to north-west India (1.50 µg m−3) and north-east India (0.70 µg m−3) during the pre-monsoon season. Across northern India, two distinct BC modes were recorded; a mode of small BC particles (core diameter <0.16 µm and coating thickness <50 nm) and a mode of moderately coated BC (core diameter <0.22 µm and coating thickness of 50–200 nm). The IGP and north-east India locations exhibited moderately coated black carbon particles with enhanced coating thicknesses, core sizes, mass absorption cross sections, and scattering enhancement values compared to much lower values present in the north-west. The coating thickness and mass absorption cross section increased with altitude (13 %) compared to those in the boundary layer. As the monsoon arrived across the region, mass concentration of BC decreased over the central IGP and north-east locations (38 % and 28 % respectively), whereas for the north-west location BC properties remained relatively consistent. Post-monsoon onset, the coating thickness, core size, mass absorption cross section, and scattering enhancement values were all greatest over the central IGP much like the pre-monsoon season but were considerably reduced over both north-east and north-west India. Increases in mass absorption cross section through the atmospheric column were still present during the monsoon for the north-west and central IGP locations, but less so over the north-east due to lack of long-range transport aerosol aloft. Across the Indo-Gangetic Plain and north-east India during the pre-monsoon and monsoon seasons, solid-fuel (wood burning) emissions form the greatest proportion of BC with moderately coated particles. However, as the monsoon develops in the north-east there was a switch to small uncoated BC particles indicative of traffic emissions, but the solid-fuel emissions remained in the IGP into the monsoon. For both seasons in the north-west, traffic emissions form the greatest proportion of BC particles. Our findings will prove important for greater understanding of the BC physical and optical properties, with important consequences for the atmospheric radiative forcing of BC-containing particles. The findings will also help constrain the regional aerosol models for a variety of applications such as space-based remote sensing, chemistry transport modelling, air quality, and BC source and emission inventories.

Insights into characteristics of light absorbing carbonaceous aerosols over an urban location in Southeast Asia

Light absorbing carbonaceous aerosols (LACA) consisting of black carbon (BC) and brown carbon (BrC) have received considerable attention because of their climate and health implications, but their sources, characteristics and fates remain unclear in Southeast Asia (SEA). In this study, we investigated spatio-temporal characteristics of LACA, their radiative properties and potential sources in Singapore under different weather conditions. Hourly BC concentrations, measured from May 2017 to March 2018, ranged from 0.31 μg/m3 to 14.37 μg/m3 with the mean value being 2.44 ± 1.51 μg/m3. High mass concentrations of BC were observed during the south-west monsoon (SWM, 2.60 ± 1.56 μg/m3) while relatively low mass concentrations were recorded during the north-east monsoon (NEM, 1.68 ± 0.96 μg/m3). There was a shift in the Absorption Ångström exponent (AAE) from 1.1 to 1.4 when the origin of LACA changed from fossil fuel (FF) to biomass burning (BB) combustion. This shift is attributed to the presence of secondary BrC in LACA, derived from transboundary BB emissions during the SWM. Lower AAE values were observed when local traffic emissions were dominant during the NEM. This explanation is supported by measurements of water-soluble organic carbon (WSOC) in LACA and the corresponding AAE values determined at 365 nm using a UV–vis spectrophotometer. The AAE values, indicative of the presence of brown carbon (BrC), showed that photochemically aged LACA contribute to an enhancement in the light absorption of aerosols. In addition, spatio-temporal characteristics of BC in the intra-urban environment of Singapore were investigated across diverse outdoor and indoor microenvironments. High variability of BC was evident across these microenvironments. Several air pollution hotspots with elevated BC concentrations were identified. Overall, the results stress a need to control anthropogenic emissions of BC and BrC in order to mitigate near-term climate change impacts and provide health benefits.

Review of recent literature on the light absorption properties of black carbon: Refractive index, mass absorption cross section, and absorption function

Knowledge of the optical properties of soot black carbon (BC) is required for the prediction of the radiative effects of freshly-emitted and aged BC particles. Here we review BC mass absorption cross section (MAC) and absorption function E(m) measurements, focusing on freshly-emitted BC. First, we review recently reported MACs at 550 nm wavelength as obtained from direct measurements of particulate absorption and mass concentration; we find an average of 8.0 ± 0.7 m2/g from ten measurements, not significantly higher (p > 0.26) than the widely used MAC of 7.5 ± 1.2 m2/g recommended by Bond and Bergstrom [Bond, T. C., and R. W. Bergstrom. 2006. Light absorption by carbonaceous particles: An investigative review. Aerosol Sci. Technol. 40(1):27–67]. Second, we review recently reported E(m), whose retrieval is more complex due to the need to combine measurements with numerical models to estimate the contribution of scattering to extinction. Third, we review recent numerical studies that have aimed to predict the BC MAC using various complex refractive indices (m = n + ik). Most of these studies have used m = 1.95 + 0.79i recommended by Bond and Bergstrom (2006), yet failed to predict a MAC as high as 7.5 or 8.0 m2/g at 550 nm wavelength. Fourth, we summarize a selected range of alternative values of m that has been reported by recent studies and place them in the context of measurements using a contour plot of E(m) on the n–k plane. We show that the widely used m = 1.95 + 0.79i corresponds to an E(m) that is too low to be consistent with the measured MAC values. We conclude that the E(m) of BC in the visible and near infrared should be greater than 0.32, and that the commonly used BC models or the refractive index, or both, are still in need of improvement.

Characterization and source apportionment of black carbon aerosol in the Nanjing Jiangbei New Area based on two years of measurements from Aethalometer

Black carbon (BC) aerosols were measured using a seven channel Aethalometer at a suburban site of Nanjing, East China from January 2015 to December 2016 to study its temporal variations and quantify the magnitude of BC from fossil fuel (BCff) and biomass burning (BCbb) sources. The mean BC mass concentration was observed to be 2200 ± 1309 ng/m3 at the sampling site during the entire observation period, with the highest (lowest) concentrations found in the winter (summer and spring). A distinct diurnal variations in BC revealed with two maximum peaks occurred between 06:00 and 09:00 local time (LT) and 19:00 and 22:00 LT in all four seasons, was correlated with source emissions, meteorology, and dynamics of the atmospheric boundary layer. A significant seasonality was observed in the absorption Ångström exponent (α) with higher in spring and winter seasons, and lower during the summer. Further, it is evident that the contribution of BCff (BCff%) dominated during the observation period with the mean contributions of BCff % and BCbb% to the BC were found to be ~81% and 19%, respectively. Similar to α, BCbb% also exhibited high fractions in spring and winter suggests an enhanced contribution from biomass burning sources, and a low in summer. The results from both the potential source contribution function (PSCF) and concentration weighted trajectory (CWT) models indicated that the air masses originating from the northern Zhejiang and Anhui provinces were the potential source areas responsible for the high BC concentrations attributed from agricultural waste burning in Nanjing.

Assessment of regional aerosol radiative effects under the SWAAMI campaign – Part 1: Quality-enhanced estimation of columnar aerosol extinction and absorption over the Indian subcontinent

Abstract. Improving the accuracy of regional aerosol climate impact assessment calls for improvement in the accuracy of regional aerosol radiative effect (ARE) estimation. One of the most important means of achieving this is to use spatially homogeneous and temporally continuous datasets of critical aerosol properties, such as spectral aerosol optical depth (AOD) and single scattering albedo (SSA), which are the most important parameters for estimating aerosol radiative effects. However, observations do not provide the above; the space-borne observations though provide wide spatial coverage, are temporal snapshots and suffer from possible sensor degradation over extended periods. On the other hand, the ground-based measurements provide more accurate and temporally continuous data but are spatially near-point observations. Realizing the need for spatially homogeneous and temporally continuous datasets on one hand and the near non-existence of such data over the south Asian region (which is one of the regions where aerosols show large heterogeneity in most of their properties), construction of accurate gridded aerosol products by synthesizing the long-term space-borne and ground-based data has been taken up as an important objective of the South West Asian Aerosol Monsoon Interactions (SWAAMI), a joint Indo-UK field campaign, aiming at characterizing aerosol–monsoon links and their variabilities over the Indian region. In Part 1 of this two-part paper, we present spatially homogeneous gridded datasets of AOD and absorption aerosol optical depth (AAOD), generated for the first time over this region. These data products are developed by merging the highly accurate aerosol measurements from the dense networks of 44 (for AOD) and 34 (for AAOD) ground-based observatories of Aerosol Radiative Forcing over India NETwork (ARFINET) and AErosol RObotic NETwork (AERONET) spread across the Indian region, with satellite-retrieved AOD and AAOD, following statistical assimilation schemes. The satellite data used for AOD assimilation include AODs retrieved from MODerate Imaging Spectroradiometer (MODIS) and Multiangle Imaging SpectroRadiometer (MISR) over the same domain. For AAOD, the ground-based black carbon (BC) mass concentration measurements from the network of 34 ARFINET observatories and satellite-based (Kalpana-1, INSAT-3A) infrared (IR) radiance measurements are blended with gridded AAODs (500 nm, monthly mean) derived from Ozone Monitoring Instrument (OMI)-retrieved AAODs (at 354 and 388 nm). The details of the assimilation methods and the gridded datasets generated are presented in this paper. The merged gridded AOD and AAOD products thus generated are validated against the data from independent ground-based observatories, which were not used for the assimilation process but are representative of different subregions of the complex domain. This validation exercise revealed that the independent ground-based measurements are better confirmed by merged datasets than the respective satellite products. As ensured by assimilation techniques employed, the uncertainties in merged AODs and AAODs are significantly less than those in corresponding satellite products. These merged products also all exhibit important large-scale spatial and temporal features which are already reported for this region. Nonetheless, the merged AODs and AAODs are significantly different in magnitude from the respective satellite products. On the background of above-mentioned quality enhancements demonstrated by merged products, we have employed them for deriving the columnar SSA and analysed its spatiotemporal characteristics. The columnar SSA thus derived has demonstrated distinct seasonal variation over various representative subregions of the study domain. The uncertainties in the derived SSA are observed to be substantially less than those in OMI SSA. On the backdrop of these benefits, the merged datasets are employed for the estimation of regional aerosol radiative effects (direct), the results of which would be presented in a companion paper, Part 2 of this two-part paper.

Impact of Outdoor Air Pollution on Indoor Air Quality in Low-Income Homes during Wildfire Seasons.

Indoor and outdoor number concentrations of fine particulate matter (PM2.5), black carbon (BC), carbon monoxide (CO), and nitrogen dioxide (NO2) were monitored continuously for two to seven days in 28 low-income homes in Denver, Colorado, during the 2016 and 2017 wildfire seasons. In the absence of indoor sources, all outdoor pollutant concentrations were higher than indoors except for CO. Results showed that long-range wildfire plumes elevated median indoor PM2.5 concentrations by up to 4.6 times higher than outdoors. BC, CO, and NO2 mass concentrations were higher indoors in homes closer to roadways compared to those further away. Four of the homes with mechanical ventilation systems had 18% higher indoor/outdoor (I/O) ratios of PM2.5 and 4% higher I/O ratios of BC compared to other homes. Homes with exhaust stove hoods had PM2.5 I/O ratios 49% less than the homes with recirculating hoods and 55% less than the homes with no stove hoods installed. Homes with windows open for more than 12 hours a day during sampling had indoor BC 2.4 times higher than homes with windows closed. This study provides evidence that long-range wildfire plumes, road proximity, and occupant behavior have a combined effect on indoor air quality in low-income homes.